Thursday, August 30, 2007

Revisiting the 20035.7-liter Hemi V8

The 2003 5.7-litre Hemi V8

The technology of the latest Hemi - and a quick look at the past

by Julian Edgar

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When in 1997 DaimlerChrysler was evaluating future engine directions, the company realised that the then-current 5.9-litre V8 used in US market trucks was likely to be outgunned in performance and economy by coming competitors. Studies were made of possible replacement designs, including iterations with 2, 3 and 4 valves per cylinder, overhead valves and overhead camshafts, the latter including single camshaft and double camshaft designs.

However, in the end, the company chose a 2-valves-per-cylinder, overhead valve, hemispherical combustion chamber approach. The 5.7-litre Hemi was introduced for the 2003 model year Ram series of pick-up trucks.

So what makes this engine better than the engines of 20, 30, and 40 years ago that the specifications appear so similar to?

New Design Aims

DaimlerChrysler engineers had these aims for the new engine:

  • engine performance
  • noise/vibration/harshness (NVH)
  • reliability and serviceability
  • leak free
  • fuel economy
  • exhaust emissions
  • quality
  • mass reduction
  • "no touch"
  • reduced part count

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The 5.7-litre engine that resulted was an OHV 90-degree V8 using an iron block and aluminium cylinder heads. Each of the hemispherical combustion chambers featured two spark plugs and two valves. The intake manifold used a composite (plastic) construction. Maximum power of 257kW was developed at 5600 rpm and a peak torque of 508Nm was available at 4400 rpm. Despite that relatively high peak torque rpm, the big engine developed 412Nm at just 1200 rpm. Mass of the engine was 242kg.

But let's have a look at the design in more detail.


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The block was cast from simple grey cast iron. It used a dry valley and deep skirt design, with the cam mounted high (for an OHV engine!) in the block. Potential leak sources through welch plugs were eliminated - the water jacket of the block didn't have any. As a result of this approach, the open-deck block required large openings for easy sand removal after casting.

The main bearing caps were made from powder metal and used cross-bolting with a single M8 bolt each side. A 99.5mm bore and a 90.9mm stroke were used, with a bore spacing of 113.3mm.

Extensive use of Computer Aided Engineering (CAE) was made in the design of the block, primarily in order that it be made as light as possible while still being cast from iron. In addition, the "no touch" goal was addressed - this referred to a manufacturing process that prevented any finished surface from being touched once it had been machined or ground.


The heads were cast from A319F aluminium alloy and each had a mass of approximately 13.6kg, a substantial 9kg reduction over the previous 5.9-litre engine. The heads were bolted to the block using M12 bolts spaced around the bores and M8 bolts near the intake manifold. Intake valves were 50.8mm in diameter and exhaust valves, 39.4mm. The intakes were angled at 18 degrees relative to the head surface, while the exhaust valves were at 16.5 degrees. The valve seats and valve guides were made from powdered metal.

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Intake and exhaust flows were comprehensively tested and on the inlet reached 118 litres/second (at 6.2 kPa pressure differential) at 12mm of valve lift, and on the exhaust, 85 litres/second at the same lift and pressure differential.

The valve bridge was kept wide in order that adequate cooling flow could be maintained; this was seen as especially important in the truck applications of the engine where it could be expected to be working hard for long periods.

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To reduce the likelihood of leaks, the spark plugs were mounted in cast-in towers. A previous design approach used pressed-in spark plug tubes but the chance of leakage occurring past the seals was seen as too great.

CAE was used to optimise the coolant flow within the heads, which was primarily a 'U-flow' beginning at the rear of each head and exiting at the front into the cylinder block. Using Computational Fluid Dynamics, fillets and ribs were added to the internal head coolant passages in order that higher velocity flows occurred in critical cooling zones.

The cylinder head gaskets were three-layer stainless steel with a compressed thickness of 0.7mm.

Front Cover

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The front cover, which sealed the front of the block and sump, was die-cast from SAE A380 aluminium. The alternator, water pump, air-conditioning compressor, power steering pump and belt idler were all mounted on the cover. Careful design achieved lower levels of vibration for the mounting points of the air-conditioning compressor and alternator.

The water pump was also die-cast from SAE A380 alloy. It used an internal coolant bypass and an 89mm diameter, fully-shrouded nylon impeller.

Intake Manifold

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The intake manifold assembly comprised a pre-supplied module containing the injectors, an 80-mm diameter electronic throttle butterfly, intake manifold, sound-damping cover, the PCV system, MAP sensor and engine wring harness. With all these components integrated into the one unit, over the previous engine design the final assembly part count decreased from 26 to 2.

The intake system, made from seven sub-assemblies formed from Nylon 6, used an 11.3 litre plenum volume and intake runners that were each 273mm long. Each runner tapered from a diameter of 50mm at the plenum to 43mm at the heads. The intake plenum volume was kept low to "achieve excellent throttle response and minimise idle speed variation". When compared with intake port flow alone, the intake system caused a 10 per cent flow restriction at maximum power.

To reduce NVH, the intake assembly used a 3-chamber Helmholtz intake resonator (see Driving Emotion), extensive ribbing and a minimum 3mm wall thickness on all exposed surfaces. A soundproofing pad was also attached to the base of the assembly, across the engine's valley.

Exhaust Manifolds

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Despite looking quite basic, the engineers claimed that the exhaust manifolds were the result of extensive and detailed design. Each was designed to provide maximum flow capacity within the constraints of taking up minimal room, protecting under-bonnet components from heat, and having a low thermal inertia so that the cat converters could be quickly heated. The claimed life of the manifolds was 241,395km. (At 241,396km they crack?!) The manifolds were cast from high silicon-molybdenum ductile iron; when compared with 4-2-1 extractors, the manifolds reduced peak power by only 2.2 per cent.


A geroter style pump, driven from the timing chain crankshaft sprocket, provided oil flow to the lubrication system. The pump was made from die-cast aluminium (housing), powdered metal (geroters) and cast iron (cover plate). It displaced 1.1 cubic inches per revolution and was sized to allow for "future oil system controlled devices" (perhaps variable cam timing or variable cylinder cut-off), worked at a relief pressure of 55 psi and used 5W-30 oil. The oil capacity was 7 quarts; smaller volumes created aeration problems at high rpm.


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The crank was cast from nodular iron. It used main journals that were 65mm in diameter, with the small-end journals 54mm. The design included deep-rolled undercut fillets to improve fatigue strength. A vibration damper was a press-fit on the nose of the crank; no keyway was used as part of the 'leak-free' design goal.


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The con-rods were manufactured from powdered metal and featured cracked big-ends. Each rod had a mass of 597 grams (including the bolts) and was controlled such that no rod varied from this figure by more than plus/minus 5 grams.


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The pistons were cast from eutectic alloy and each had a mass of 413 grams. Each slightly domed piston was coated with a graphite-based product on the skirts to reduce scuffing. The top land was reduced to 3mm to minimise crevice volume and so hydrocarbon emissions. The gudgeon pin was a press-fit in the con-rod.


It is significant that despite starting with the proverbial 'clean sheet of paper', DaimlerChrysler engineers decided to go with a design that was very conventional in its engineering fundamentals. The engineers saw the advantages of the 5.7-litre Hemi design as:

  • Class-leading performance with 41 per cent more power, 46 per cent greater power density and a torque increase of 12 per cent over the previous design
  • Competitive fuel economy, high combustion stability and low specific exhaust emissions
  • Highly integrated intake manifold assembly

SAE paper 2002-01-2815: The New DaimlerChrysler Corporation 5.7 HEMI V8 Engine

Hemis of the Past

The 5.7-litre is the fifth OHV Hemi Chrysler V8. Here are the previous designs:


Model Year


Chrysler Fire Power V8


331 cid

DeSoto Fire Dome V8


276 cid

Dodge Red Ram V8


241 cid

Dodge/Plymouth V8


426 cid

The detail in the comparison between the '66 426 and the new 5.7-litre show some startling changes, even in the basic specifications.


New 5.7L

1966 426 HEMI

Displacement (cc)



Bore (mm)



Stroke (mm)



Bore/Stroke Ratio



Compression Ratio

9.6: 1


Bore Spacing (mm)



Bank Offset (mm)



Block Length (mm)



Block Deck Height (mm)



Connecting Rod Length (mm)



Piston Compression Height (mm)



Rod Length/Crank Radius



Intake Valve Diameter




Exhaust Valve Diameter (mm)



Included Valve Angle (deg.)



Combustion Chamber Volume (cc)



Intake Valve Lift (mm)



Exhaust Valve Lift (mm)



Mass (kg)




Courtesy of DaimlerChrysler, Some Hemi-Powered Cars...

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1955 CHRYSLER 300

With a HEMI® engine mated to the new Powerflite automatic transmission, styling by Virgil Exner, plus power steering and power brakes, Chrysler product planners realized they had the ingredients for a car that in Italy would be called a Gran Turismo - a sport tourer. Despite a two-ton body and a luxurious cabin, a stock 300 powered by its 300 hp dual four-barrel, 331 c.i.d. HEMI® could nudge 125 mph. The Chrysler 300 was a performance blueblood from the beginning and is highly sought by collectors today.

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When NASCAR introduced a new "Experimental" class for its Speedweeks at Daytona Beach in 1957, Wally Parks, co-founder of both Hot Rod Magazine and of the National Hot Rod Association, decided he'd play, too. Although the class was intended primarily for company-backed entries, Parks, then editor of Hot Road Magazine, and the magazine's technical writer Ray Brock "borrowed" a new Plymouth Savoy right off the line at Chrysler's Los Angeles plant. The name came from the Plymouth ad campaign at the time, "Suddenly It's 1960!"

A Chrysler HEMI® was modified to 389 c.i.d. and special exhaust headers added. Firestone racing tyres, roll bars and safety equipment were installed and the front end modified. Towed to the starting line at Daytona, it had never run under its own power. Nevertheless Parks hit 166.898 mph, and the two-way average over two miles was 159.893 mph! This was the fastest time run for the week, and was then the fastest closed-car run ever recorded at Daytona. In the process, Plymouth beat 13 other makes. Later that year, with a new HEMI® from Dean Moon, Ray Brock got the Plymouth to 183 mph at Bonneville.

After being reconverted to street use, the car was sold and disappeared. In 1995 Parks, then age 83, decided to recreate "Suddenly," but the body used was not a hardtop, which Parks felt was not authentic. Brock then gave him a hardtop as a birthday present and it became the source of the correct "postless" body. Parks has run "Suddenly II" a number of times in exhibition competition.


1/4 mile/7.640 sec. 178.57mph

Following in the slick marks left by Don Garlits' Swamp Rat, HEMI® engines were a common choice for the supercharged, lightweight dragsters that ran in the AA/fuel class, burning nitromethane/alcohol mixtures. The rugged design of the HEMI® could withstand even the 1,200 to 1,500 hp generated by the cars. This dragster built in 1967 used a 1957 392 c.i.d. HEMI® as the starting point. It is equipped with Hilborn fuel injection and a Roots-type 8-71 supercharger. A Hayes sliding clutch couples the drive shaft directly to the solid rear axle. There is no transmission. Wheels are 16-inch, polished American mags with M & H racing slicks. Dubbed "Probe," this car competed in the Midwest between 1967-1969 for the Phil Goulet (tuning) and Ray DeNoble (driver) team.

Logghe Stamping Company of Warren, Mich., fabricated Probe's frame of chrome-molybdenum tubing; the aluminium body was fabricated by Al Bergler.

Length: 220"
Wheelbase: 185"
Max. Width: 48"
Minimum Ground Clearance: 3"

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The Silver Bullet drag car is powered by a 426 HEMI® bored and stroked to 487 c.i.d. with other modifications that permit quarter-mile times in the mid-10-second range with top speed close to 140 mph.

The saga of the "Silver Bullet" began with Jimmy Addison, the manager of a Sunoco station on Woodward Avenue, and a man known for his skill in setting up a car for drag racing competition. He was also famed as a street racer, driving a 1962 Max Wedge Dodge. Addison was respected by Chrysler performance engineers, who helped him acquire a 1967 Plymouth Belvedere GTX used to set 440 four-bbl Wedge component combinations.

Connections at Chrysler also helped Addison build a bored and stroked HEMI® with aluminium heads, special cam, carburettors and pistons to replace the Wedge. The HEMI® was matched with a Torqueflight automatic transmission fitted with a 4,000 rpm stall converter, special rear end ratios and 12-inch slicks on the rear tyres. Addison installed fibreglass fenders, doors, hood and decklid to drop the overall weight by some 500 pounds. Flared rear fenders were necessary due to the wide slicks, and the car was painted silver. When journalist Ro McGonegal wrote about the car for the September 1971 issue of Car Craft magazine, he supplied the name - the "Silver Bullet."

Retired from racing, the "Silver Bullet" was found and restored by noted Mopar muscle car collector Harold Sullivan.

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